Dentifrice polishing agents



United States Patent 3,269,814 DENTHFRICE POLISHING AGENTS Lowell E.Netherton, Park Forest, and Reginald E.

Vanstrom, Greta, IlL, assignors to Stauifer Chemical Company, New York,N.Y., a corporation of Delaware No Drawing. Filed Feb. 26, 1962, Ser.No. 175,735 7 Claims. (Cl. 51-307) This application is acontinuation-in-part of our copending application, Serial No. 83,938,filed January 23, 1961, now abandoned.

The present invention is directed to intimate mixtures of condensedphosphates suitable as dentifrice polishing agents in formulationsdesigned for application of active fluorides to the teeth, and theirmethod of manufacture.

In recent years, considerable effort has been devoted to evaluating andperfecting the means for applying soluble fluorides to human teeth. Itis now generally recognized that the fluoride ion (supplied from asoluble fluoride salt such as SnF or NaF) tends to lessen or minimizedental caries when applied either topically to the teeth from aconcentrated solution or paste, or when incorporated in municipaldrinking Water.

Nevertheless, the use of soluble fluorides in toothpastes ortoothpowders gives rise to a problem of compatibility. Briefly, it isdifiicult to prepare a polishing agent ingredient for toothpastes orpowders which, when combined in a formulation together with a fluoride,will not react with the fluoride and diminish its effectiveness as adecay preventative. In fact, most of the conventional polishing agentsused for many years in non-fluoride pastes and powders willsubstantially inactivate the fluoride ion making it unavailable forlater reaction at the outer layers of human teeth, i.e., with thehydroxylapatite component of tooth enamel and dentin.

Most of the major fluoride dentifrice formulators have heretoforeselected polishing ingredients from among the Well-known fairlyinsoluble phosphates and polyphosphates, primarily calcium pyrophosphate(see, e.g., US. Patent 2,876,166) and insoluble sodium metaphosphate, inan effort to achieve the highest degree of compatibility possible withcommercially available materials.

It is also generally recognized that the tin (II) ion, when suppliedfrom stannous fluoride, is effective in reducing tooth decay. Recentstudies have revealed that the stannous or tin (11) ion reacts, likefluoride ion, at the surface or slightly within tooth enamel to form acomplex tin compound, probably tin (II) hydroxyorthophosphate, see,e.g., Journal of Dental Research, vol. 4, No. 6. Nov. Dec. 1961, pp.11994210, and that erupted human teeth are deficient in tin in theoutermost layers, containing virtually none in deeper layers, ibid, p.1200.

But again, like the fluoride ion, tin (II) tends to react when combinedwith other chemical ingredients, thereby becoming inactivated orunavailable when applied to the teeth. It is therefore-obvious thatstannous fluoride, prob ably the most effective of the present dayfluoride decay preventatives, must be utilized in a compatible medium ifit is to be effective at the time of topical application to the teeth.When it is applied from a toothpaste, the polishing agent ingredienttherein must be unreactive, the degree of compatibility being aquantitative measurement of the suitability of the polishing agent foruse with tin (ID-containing formulations.

It is an object of this invention to furnish improved inorganicphosphate dentifrice polishing agents.

Another object of this invention is to furnish inorganic phosphatedentifrice polishing agents which, when included in afluoride-containing dentifrice preparation, will permit a largepercentage of the originally added fluoride constituent to remain in anavailable, ionized state.

3,269,8l4 Patented August 30, 1966 A further object of this invention isto furnish inorganic phosphate dentifrice polishing agents which, whenincluded in a tin fluoride-containing dentifrice preparation, willpermit a large percentage of both the tin and the fluoride ions toremain in an available, ionized state.

Still another object of this invention is to furnish a method by whichthe fluoride-compatible phosphates of the invention may be manufactured.

Other objects will readily appear to those familiar with the art as thedescription proceeds.

We have now discovered that the addition of an acidic phosphate, or aphosphate capable of passing through an acidic state during hydrolysisor heating, to a dibasic alkaline earth metal orthophosphate yields,upon heating, a phosphate dentifrice polishing composition havingimproved compatibility toward fluoride and tin (II) ions when combinedtherewith in an aqueous medium. As an illustration, an intimate mixturecontaining about 1% monobasic alkaline earth metal orthophosphate, e.g.,monocalcium orthophosphate, monohydrate with the remainder dicalciumorthophosphate, dihydrate may be heated at between about 300 C. and 1100C. to yield a polishing agent having greater compatibility thanheretofore typical of the separately heated compounds or mechanicalmixtures thereof. As used hereafter, the term acidic material isintended to refer to both the initially acidic compounds and those whichpass through an acidic state, as defined more precisely, infra.

By analysis, all of the compositions produced by the method of thepresent invention will be found to comprise a predominant proportion ofalkaline earth metal pyrophosphate, e.g., Ca P O Mg P O etc., the usualproduct of high temperature conversion of a dibasic alkaline earth metalorthophosphate, and a minor amount of one or more other phosphates. Thecomposition of these latter phosphates will obviously depend upon whichacidic material is selected for addition to the dibasic alkaline earthmetal orthophosphate. Although none of the phosphates except thealkaline earth metal pyrophosphates have yet been isolated andidentified precisely in terms of chemical formula or structure, it hasbeen discovered that most, if not all, are more water soluble than thealkaline earth metal pyrophosphate with which they are concurrentlyproduced.

The greatest compatibility, at least the greatest improvement thereof,is usually noted Where only a relatively small percentage of the acidicmaterial is added. For example, the heating of dimagnesiumorthophosphate, trihydrate with about 1% monomagnesium orthophosphate,dihydrate added yields a product having better fluoride compatibilitythan magnesium pyrophosphate prepared exclusively from pure dimagnesiumorthophosphate, trihydrate. On the other hand, if large percentages, forinstance about 40% or more of the additive is used, the fluoridecompatibility will be found to decrease from its optimum value.

A particularly important feature of the invention is our finding thatcompatibility improves only if the acidic material is added beforeheating. Although We do not wish to be bound to any specific theory, anappreciable quantity of the acidic material probably reacts duringheating with a stoichiometrically equivalent proportion of dibasicalkaline earth metal orthophosphate. Because of practical limitations,ideal contact between the acidic material and the dibasic alkaline earthmetal orthophosphate (on the molecular or ionic level) is impossible,especially where the acidic material is in a particulate form, andtherefore not all of the acidic material is thought to reactintermolecularly with the dibasic alkaline earth metal orthophosphate.That which does not so react is nevertheless changed chemically byelimination of molecular water, e.g., a monocalcium orthophosphate mightconvert to a calcium metaphosphate. Thus characterization of the productis rendered even more complicated by virtue of inclusion therein of someextremely insoluble metaphosphate which, because they represent a veryminor proportion of the total mixture, cannot be easily found byordinary analytical methods such as X-ray powder diffraction patterns.The product may also include amorphous phosphates which cannot beroutinely detected by X-ray diffraction patterns. All of thesepossibilities make it virtually impossible to ascribe percentages to theindividual components of the product.

Due to formation by interand intramolecular dehydration, the compoundscontained in the compositions of this invention are intimately combined,in what may be called an intraparticulate mixture. Single particles maycontain two or even more condensed phosphates which cannot be separatedby mechanical means. The use herein of the term intimate mixtures istherefore intended to describe these pyrogenetically formed mixtures ofcondensed phosphate and to distinguish the same from simple physicaladmixtures.

The starting materials of the present invention are wellknown chemicalcompounds which, in most case, are available today in commercialquantities. Both the hydrates and the anhydrous forms of these startingmaterials, especially the dibasic alkaline earth metal orthophosphates,are suitable (the hydrated forms lose water of crystallization easily atthe high temperatures of the invention to yield the anhydrous forms).Further, the so-called stabilized calcium orthophosphates (such asdescribed in United States Patent 3,066,056), which are prepared bymethods that comprise the in situ addition of polyor pyrophosphoricacid, are also suitable starting materials. However, all other factorsbeing equal, unstabilized dicalcium orthophosphate will furnish a morecompatible polishing composition than the stabilized material when saidcomposition is prepared by the method of the present invention.

The di'basic alkaline earth metal orthophosphates of the inventioninclude those of calcium, magnesium, beryllium, strontium, and barium.But, by virtue of their availability and low cost, the calcium andmagnesium orthophosphates are especially preferred. The acidic materialsare likewise readily available compounds. Those which are initiallyacidic include monocalcium orthophosphate, monomagnesium orthophosphate,orthophosphoric acid, pyrophosphori acid, sodium acid pyrophosphate,monosodium orthophosphate, urea phosphate, monoammonium orthophosphate,monopotassium orthophosphate and monolithium orthophosphate. Both acidicalkali and alkaline earth metal primary orthophosphate or mixed saltsare included generally. Materials which are suitable by virtue offorming an acidic phosphate residue when heated at the temperatures ofour method include organic amine and basic ammonium phosphates such astetraamonium pyrophosphate, sodium ammonium phosphate, and diammoniumphosphate. These compounds presumably undergo decomposition at hightemperatures forming a residue which reacts much the same as thoseadditives which are initially acidic. The remaining class of additivesconsists of hydrolyzable phosphates which tend to leave an acidicresidue under the conditions of the present method. These have beenfound to include the alkali and alkaline earth metal metaphosphates suchas those of calcium, sodium, magnesium, and potassium.

The following specific examples are given to further illustrate theinvention and no unnecessary limitations should be implied therefrom.

Example 1 A large batch of finely milled dicalcium orthophosphatedihydrate was divided into individual portions weighing 400 grams each.To prepare the test sample, one of these 400 gram portions was placed ina stoppered bottle together with 4 grams of monomagnesium orthophosphatedihydrate and the bottle was thereafter vigorously agitated tothoroughly mix the phosphates. A control sample of 400 grams ofdicalcium orthophosphate dihydrate, obtained from the same batch as thatin the foregoing test sample, was also selected for this experiment.Each sample was spread out thinly on a No. 7 evaporating dish which wasplaced in .a mufile heater maintained at a temperature of about 650 C.After heating for four hours in the muflle, during which time thetemperature was held steady at 650 C., the samples were removed, cooledto room temperature and milled in a Raymond hammer mill. The sampleswere then tested for tin (II) compatibility by the procedure outlinedinfra. The polishing agent prepared from the test sample was found 58.7%compatible, while that prepared fro-m the control sample showed, by thesame test, a compatibility of 37.3%.

Example 2 Using the same method as described in Example 1, a test samplewas prepared containing a mixture of 4 grams of monoammonium phosphateand 400 grams of dicalcium orthophosphate dihydrate. The mixture washeated together with a control sample of pure dicalcium orthophosphatein a mufile heater for four hours at about 650 C. Analysis showed thatthe polishing agents produced from the test sample and control samplewere 57.8% and 43.5% compatible to tin (II), respectively.

In order to evaluate the commercial feasibility of pre paring thepolishing agents of the invention, pilot runs were conducted insmall-scale, industrial-type apparatus. Generally, it was found that themethod adapts easily (even when using the rather specialized techniquesof fiuidizati-on) to commercial manufacture, and allows a high degree ofquality control, a characteristic of material significance in suchapplication.

Examples of pilot runs made to explore the commercial aspects of ourmethod will now be presented.

Example 3 Several hundred pounds of a dicalcium orthophosphate feed wasfirst prepared by adding a stoichiometric quantity of lime to a diluteorthophosphoric acid solution and collecting the precipitate. This wetorthophosphate was dried in a standard rotary drier and then mixed with1% of a similarly prepared batch of monocalcium orthophosphatemonohydrate in a ribbon blender. About 220 lbs. of the mixture oforthophosphates were charged to the bed chamber of a 2 ft. diameterfluidization reactor, after which fiuidization was commenced by passinggases upward through the material. The bed uniformly expanded to adense, turbulent fluidized state. A hydrocarbon fuel was burned tosupply hot gases to concurrently heat and fluidize the bed; combustionrate was adjusted to maintain the bed at a temperature within the rangeof 650 to 700 C. After about nine hours of heating, additional mixedcalcium orthophosphates were fed (through a screw feeder) to the bed andat the same time a stoichiometrically equivalent quantity of convertedmaterial was withdrawn. The feed rate was controlled to give a retentiontime of approximately nine to twelve hours, thereby averaging about 21lbs. of feed per hour. Continuous feeding and product withdrawal wereaccomplished over a period of several weeks without fouling theapparatus. Samples of product taken periodically during this time showedcompatibilities ranging from about 12% to 57% higher than for similarpolishing agents produced from pure dicalcium orthophosphate dihydratein the same apparatus. The product was also found to be a freefiowing,finely divided material equaling or exceeding normal commercialrequirements.

Example 4 A slurry containing 50% solids and weighing 500 lbs. wasprepared from a mixture of 99% dicalcium orthophosphate and 1%monocalcium orthophosphate. Using a positive displacement pump theslurry was conunder identical conditions (static heating in ovens at 500to 900 C.) for the same period of time.

The data of Table I are given especially for the purpose of showing twoeffects, namely that (1) small percentages of the acidic material willcause an appreciable improvement in compatibility and (2) a wide rangeof acidic materials may be used. Differences between the compatibilitiesof the various control samples prepared from CaHPO -2H O areattributable mainly to the duration of heating.

TABLE I Tin (II) Compatibility oi Heated (con- Percent Composition Feedbefore Heating verted) feted,

percen Bicalcium orgopgospgaze, gigygrateu (Control sample) 33. 2 icacium or op osp a e i y rate Monoealeinm orthophosphate, monohydrate}(Test Sample) 2 gicalclum orgpopgospgaitbe, giygrate (Control sample)32. 3 ica cium or 10p osp a e y rate Calcium metaphosphateflju }(Testsample) 8 Dicalcium orthophosphate, d1hydrate (Control sample) 37. 3Dicalcium orthophosphate, dihydrate (Te t m 16) 58 7 1.0 Monomagnesiumorthophosphate, dihydrate 5 5a p 5 0 0 lgiealcium orglfiopgospgategilhygrazeun (Control sample) 43. 5

. ica cium or op osp ate iiy ra e 1.0 Monoammonium phosphate }TestSample) 8 g$80.0. gicalcium ortgopgospliate, gigygraten (Control sample)40. 2

.0... ica cium ort op osp 1a e, i y rate. 1.0 Monosodium orthophosphate}(Test Sample) 5 $8060" gicallcium orgiilopgospgate, gigygrateun(Control sample) 45. 5

. ica cium or op osp ate, i y rate. 1.0 Orthophosphoric acid }(T0Stsample) 9 100.0 Dicalcium orthophosphate, dihydrate (Control sample) 41.3 $960. licalcigm OfilIhOpllOSPl'late, dihydrate }(Test SamPe) 58 2 reaposp ate 1 800 gimagnesium ortgopgosphate, trigygra (Control sample) 15.6 t .0 imagnesium ort 0p osphate tri y rate 1.0 Monomagnesiumorthophosphate, dihydrate }(Test Sample) 2 Example 5 The effect ofhigher percentages of the acidic addi- In order to determine the effectsof storage upon mixed phosphate polishing agents the following test wasaccomplished. By the method described in Example 1, a feed mixturecontaining 50% CaHPO -2H O, 40%

MgI-IPO- 3H O and MgH (PO.;) -2H O was prepared and calcined. It shouldbe noted that this mixture contained only 10% acidic material within thedefinitions of this specification. After calcination, a portion of themixed polishing agent was tested and found to have a tin (II)compatibility of 61.9%. The remaining portion was placed in storage atroom temperature. After sixty days of storage the sample was found tohave a tin (II) compatibility of 51.9%, although at this time thefluoride ion concentration was found to be 74% of theory.

The procedure followed for determining both tin (II) and fluoridecompatibilities involves placing a measured quantity of phosphatepolishing agent in a flask, adding thereto some distilled watercontaining a measured quantity of stannous fluoride, and agitating theresulting slurry vigorously. After agitation the slurry is centrifugedand the supernatant liquor is tested for soluble tin (II) and fluorideby well-known analytical methods. The percentage compatibility ismeasured as the ratio of the unreacted fluoride or tin -(II) to theamount originally present.

A comparison between the tin (II) compatibilities of the compositions ofthe invention and the pure compounds of the prior art is shown in TableI wherein the composition of the feed before heating is reported on theleft of the table opposite the analytical value for compatibility of theproduct resulting from heating (converting) said feed. For each feedmixture (the test sample) there is included a control sample consistingentirely of dibasic alkaline earth metal orthophosphate. Also, eachcouple (i.e., test sample-l-control sample) was heated tive oncompatibility is illustrated in the following table.

TABLE II [(21) Calcium phosphate compositions prepared from monoc-alciumorthophosphate-dicalcium orthophosphate mixtures] Percentage feed as CaH(PO H2O (percent by weight) Tin (II) compatibility (percent) 0.0(control sample) 32.3 0.5 49.0

[ (b) Magnesium phosphate compositions prepared from monomagnesiumorthophopshate-dimagnesium orthophosphate mixtures] Percentage feed asMgH (PO -2H O (percent by weight):

Tin (II) compatibility (percent) 0.0 (control sample) 15.6 1.0 27.2

phate, a compound having a tin (II) compatibility of only 1.6% in itspure form.

' The foregoing data indicate that the maximum rate of improvement incompatibility is attained at small percentages of added acidic material,and significant improvement is seldom noted when the acidic material isThe desired calcination temperatures of this invention are essentiallythe same as heretofore normally used for conversion of dibasic alkalineearth metal orthophosphates to the pyrophosphates. As disclosed in USPatent No.

added in excess of 40% by Weight of the feed. Because 2,876,166 greatercompatibility is achieved if the phosof the detrimental effect of theadditive on various charphate feed is heated until complete conversionto the acteristics of the resulting dentifrice polishing agent (e.g.,condensed phosphates, although it is preferable to stay abrasiveness),it is preferable to limit the acidic material below the fusiontemperature. The required heating for to not more than 10% by weight ofthe feed. As for complete conversion is a rather complex function of thesmaller percentages of acidic material, addition of only 10 type ofheating procedure, temperature and time, and as 0.33% of monocalciumorthophosphate monohydrate, for such is beyond the scope of thisinvention. In general, instance, has been found to increasecompatibility in calhowever, temperatures between 300 C. and 1100 C. arecium pyrophosphate from 32.3% to 37.7%, while 0.67% satisfactory, whilea preferred temperature range for either of the additive gives a producthaving 41.5% compatibilcalcium or magnesium phosphate mixtures is 500 C.to ity. Polishing agents produced from feed having less than 700 C. Theduration of heating, while dependent upon 0.33% additive have not beenfound to give improved fluthe temperature used, may be from about one tosixoride compatibility. It is nevertheless preferable to use teen hours,preferably about three to twelve hours for at least 1% acidic materialin order to obtain uniform either calcium or magnesium phosphates.

quality and ahomogenous product. The improved compositions of thisinvention may be At the preferred proportions of acidic material andused in toothpastes, toothpowders or any aqueous media dibasic alkalineearth metal orthophosphate, the resultcontaining a soluble fluoridesuitable for oral applicaing phosphate polishing agent appears toconsist of at tion to the teeth. The fluorides with which such comleast80% to not more than about 99.5% alkaline earth positions are compatibleinclude SnF NaF, ZnF SnF metal pyrophosphate, with the remainder in theform of CrF LiF, KF, CuF and NH F, while among these the other condensedphosphates. SnF and NaF are considered especially suitable.

It is highly preferable that the mixed feed be thoroughly A typicaltoothpaste containing our more compatible commingled to obtain maximumcontact between the polishing compositions may have the followingingredireactants. In order to improve contact between particulate ems;from to 50%, usually about 40%, of the materials, it is desirable thatsuch materials be in a finely compositions of the invention; from 0.04%to 1.6%, divided State, about 90100% P g through a 200 30 preferablyabout 0.4% of a soluble fluoride such as stanmesil SeTeen- However, t0some degree, improved p nous flouride; from 15% to 30% of a humectantsuch as ing agents can be Produced even from a relatively e031" 5eglycerine and/or sorbitol to suspend the solids; about 1% feedto 2% of ahinder (or gum) such as an Irish moss or car- Al'leibef feature WhiebShould be especially noted is boxylmethyl cellulose; about 1% to 2% of asynthetic that the acidic material need not have the same cationdetergent; f 1 to 2% f a preservative for h gum as the dibasic alkalineearth metal orthophosphate. By (prevents mold, etc.) such as ethylparaoept; a minor the use of feed having various cations, mixedphosphate amount up to about 1% of a fl i agent; d ffisalts such assodium calcium polyphosphates and barium Ciel-1t Water, usually f 15% to25% to expand h magneslum polyphosphates are formed in some appreciagumand thin the paste to a Suitable consistency bie p i' e 40 As shownhereinbefore, the acidic additives of the in- The acidic additives ofthe invention have also been Vention will normally comprise l than byWeight found helpful for ameliorating random varlations of fluof thetotal f d material. In most appncations, Tlde ,and/Or tin icompatibmtles- Heretofore ever, fluoride compatibility will besignificantly improved mercl'al prepfarauon Qften Welded Phosphat? P11shmg by very minor amounts of the additive, in most cases agentsespeclany p f l pyrophosphate,}, havmg 'Wldely 4.5 below 10% by weight.The usual method of addition of different compatibil ties betweensuccessive product lots, the additive material is by physical admixturewith a dry even when Prfiparatlon was accomphshed under dibasic alkalineearth metal orthophosphate, but as shown trolled cond1tions. Ostensibly,the variations were caused, above in Example 4, variations such asliquid feed are i fi m i i fi z g g 1 dlbaslg possible. Anotherpractical method of applying the ada mepar i a 0p Osp ee i 50 ditivecomprises forming a solution or slurry of the adunlformity possible withthe additives of the invention 18 d I 1 illustrated in Table III, infra.In the table it may be oban seaylng so u 5 l er Served that the productsformed from feed Containing the a statlc or agitated bed of the dibasicalkaline earth metal acidic additive showed far greater uniformity ofcompatiother methods of applymg addltlve bilities than products preparedfrom control samples made W111 be apparent from the f 9 the above dlsclosureup from the same lots of dicalcium orthophosphate, di- Theforegoing detalied deseflpilon has been given for hydrate (but notcontaining the additive). All of the feed deafness understanding y, andno unnecessary Samples shown i h t bl were t i ll h t d t limitationsshould be understood therefrom, as modifica- 650 C. for four hours toaccomplish conversion. tions will be obvious to those skilled in theart.

TABLE III Tin (II) Fluoride Percent Composition of Feed before HeatingCompat- Compatibllity, ibility,

Percent Percent Dicalciumorthophosphate,dihydrate (Control sample) 38 32irtiiliuii 2353335131?a i fliliiinaaiiiII W Sample 51 Dicalciumorthophosphate, dihydrate (Control sample) 31 24 a etatesJamessame-re;--- lwestsampe 51 46 a lssszzas tss az sates-"- 37 Miiii ocalciumort hopli osphate, n ion bhydra te }(Test Sample) 50 44 We claim:

1. Method of manufacturing a dentifrice polishing agent consisting of anintraparticulate mixture of condensed phosphates which comprises heatingat a temperature within the range from 300 C. to 1100 C., 90% and 99.67%of a dibasic alkaline earth metal orthophosphate having thoroughlycommingled therewith between- 0.33% and 10% of at least one compoundselected from the group consisting of inorganic acidic phosphates,hydrolyzable alkali and alkaline earth metal metaphosphates, andphosphates which transitionally yield inorganic acidic phosphatesresidue when heated at a temperature within the range from 300 C. to1100 C., for a time sufficient to accomplish substantially completeconversion to the condensed phosphates.

2. Method of manufacturing a dentifrice polishing agent consisting of anintraparticulate mixture of condensed phosphates which comprisesheating, at a temperature within the range from 300 C. to 1100 C.,between 90% and 99.67% of a dibasic alkaline earth metal orthophosphatehaving thoroughly commingled therewith between 0.33% and 10% of at leastone compound selected from the group consisting of monocalciumorthophosphate, calcium metaphosphate, monomagnesium orthophosphate,monoammonium orthophosphate, monosodium orthophosphate, orthophosphoricacid, pyrophosphoric acid, urea phosphate, tetraammonium pyrophosphate,sodium acid pyrophosphate, monopotassium ortho phosphate, monolithiumorthophosphate, sodium ammonium phosphate, diammonium phosphate, sodiummetaphosphate, magnesium metaphosphate, and potassium metaphosphate, fora time suflicient to accomplish substantially complete conversion to thecondensed phosphates.

3. Method of manufacturing an intraparticulate mixture of condensedcalcium phosphates which comprises heating for 3 to 12 hours, at atemperature within the range of from 500 C. to 700 C., a finely divideddicalcium orthophosphate having thoroughly commingled therewith at least0.33 but not more than 10% finely divided monocalcium orthophosphate.

4. Method of manufacturing an intraparticulate mixture of condensedmagnesium phosphates which comprises heating for 3 to 12 hours, at atemperature within the range of from 500 C. to 700 C., a finely divideddimagnesium orthophosphate having thoroughly com- 10 mingled therewithat least 0.33 but not more than 10% finely divided monomagnesiumorthophosphate.

5. An intraparticulate mixture of condensed calcium phosphates resutlingfrom substantially complete molecular dehydration of a finely dividedfeed comprising a physical admixture of between 90% and 99.67% dicalciumorthophosphate and between 0.33% and 10% monocalcium orthophosphate.

6. An intraparticulate mixture of condensed magnesium phosphatesresulting from substantially complete molecular dehydration of a finelydivided feed comprising a physical admixture of between 90% and 99.67%dimagnesium orthophosphate and between 0.33% and 10% monomagnesiumorthophosphate.

7. As a dentifrice polishing agent an intraparticulate mixture ofcondensed phosphates resulting from substantially complete moleculardehydration of a finely divided feed consisting of a physical admixtureof between 90% and 99.67% of a dibasic alkaline earth metalorthophosphate and between 0.33% and 10% of at least one compoundselected from the group consisting of monocalcium orthophosphate,calcium metaphosphate, monomagnesium orthophosphate, monoammoniumorthophosphate, monosodium orthophosphate, orthophosphoric acid,pyrophosphoric acid, urea phosphate, tetraammonium pyrophosphate, sodiumacid pyrophosphate, monopotassium orthophosphate, monolithiumorthophosphate, sodium ammnium phosphate, sodium metaphosphate,magnesium metatphosphate and potassium metaphosphate.

References Cited by the Examiner UNITED STATES PATENTS 2,876,166 3/1959Nebergall 16793 2,876,168 3/1959 Broge 167-93 2,946,725 7/1960 Norris167--93 3,029,191 4/1962 King 167--93 FOREIGN PATENTS 742,623 12/1955Great Britain.

ALEXANDER H. BRODMERKEL, Primary Examiner.

ALFRED L. LEAVI'IT, MORRIS LIEBMAN,

Examiners.

, D. J. ARNOLD, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,269,814 August 30, 1966 Lowell E. Netherton et al.

It is hereby certified that error appears in the above numbered patentrequiring Correction and that the said Letters Patent should read ascorrected below.

Column 5, line 44, for "MgHPO'BH O" read MgHPO '3H O column 9, line 12,strike out "residue".

Signed and sealed this 1st day of August 1967.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Commissioner of PatentsAttesting Officer

7. AS A DENTIFRICE POLISHING AGENT AN INTRAPARTICULATE MIXTURE OFCONDENSED PHOSPHATES RESULTING FROM SUBATANTIALLY COMPLETE MOLECULARDEHYDRATION OF A FINELY DIVIDED FEED CONSISTING OF A PHYSICAL ADMIXTUREOF BETWEEN 90% AND 99.67% OF A DIBASIC ALKALINE EARTH METALORTHOPHOSPHATE AND BETWEEN :.33% AND 10% OF AT LEAST ONE COMPOUNDSELECTED FROM THE GROUP CONSISTING OF MONOCALCIUM ORTHOPHOSPHATE,CALCIUM METAPHOSPHATE, MONOMAGNESIUM ORTHOPHOSPHATE, MONOAMMONIUMORTHOSPHOSPHATE, MONOSODIUM ORTHOPHOSPHATE, ORTHOPHOSPHORIC ACID,PYROPHOSPHORIC ACID, UREA PHOSPHATE, TETRAMMONIUM PYROPHOSPHATE, SODIUMACID PYROPHOSPHATE, MONOPOTASSIUM ORTHOPHOSPHATE, MONOLITHIUMORTHOPHOSPHATE, SODIUM AMMNUIM PHOSPHATE, SODIUM METAPHOSPHATE,MAGNESIUM METAPHOSPHATE AND POTASIUM METAPHOSPHATE.